Tap changing apparatus with improved contact structure to eliminate electrical fields across open interrupter switches

ABSTRACT

Apparatus for providing load tap changes having means for protecting the current interrupting switches from winding surge voltages. Current interrupting switches are connected to stationary contacts of a load transfer switch. Movable contacts of the load transfer switch rotate during a tap change to shunt the open and closed current interrupting switches and to eliminate the electrical fields across open current interrupting switches upon completion of the tap change.

United States Patent 9] Lingenfelter Jan. 1,1974

[ TAP CHANGING APPARATUS WITH IMPROVED CONTACT STRUCTURE TO ELIMINATE ELECTRICAL FIELDS ACROSS OPEN INTERRUPTER SWITCHES [75] Inventor: Robert C. Lingenfelter, Sharon, Pa.

[73] Assignee:v Westinghouse Electric Corp.,

' Pittsburgh, Pa.

221 Filed: July 6,1972 21 Appl. No.: 269,364

[52] [1.8. CI. 200/11 TC, 323/435 [5 1] Int. Cl. ..H01h 21/20 [58] Field of Search ZOO/ll TC; 323/435 [56] References Cited UNITED STATES PATENTS 8/1969 Norman 200/11 TC 3,643,154 2/1972 Van Riemsdijk 200/1] TC X Primary Examiner.l. R. Scott Att0rney-A. T. Stratton et a].

[5 7] ABSTRACT Apparatus for providing load tap changes having means for protecting the current interrupting switches from winding surge voltages. Current interrupting switches are connected to stationary contacts of a load transfer switch. Movable contacts of the load transfer switch rotate during a tap change to shunt the open and closed current interrupting switches and to eliminate the electrical fields across open current interrupting switches upon completion of the tap change.

8 Claims, 10 Drawing Figures PATENIEDJA'R H914 3.783.206

SHEEI NF 5 FIGQZA PAIENTEUJM I 1914 DRIVE MECHANISM FIG. 2B

TAP CHANGING APPARATUS WITH IMPROVED CONTACT STRUCTURE TO ELIMINATE ELECTRICAL FIELDS ACROSS OPEN INTERRUPTER SWITCHES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates, in general, to tap changers for electrical apparatus and, more specifically, to tap changer load transfer switches.

2. Description of the Prior Art Tap changers are usually associated with transformer windings having a plurality of taps thereon. The basic purpose of the tap changer is to connect a load to the tapped transformer winding at the correct tap position. Load tap changers must be capable of changing the tap to which the load is connected while the winding is energized and load current is flowing.

A load transfer switch is used in load tap changers to change the flow path of the load current from one tap to another tap. Vacuum switches are generally used in high-voltage load tap changers to interrupt the load current. The operation of a conventional load transfer switch containing vacuum switches or bottles is described in US. Pat. No. 3,544,884, which is assigned to the same assignee as is this invention. The patent applications filed on July 6, 1972 and Jan. 9, 1973, Ser. Nos. 269,361 and 322,236 respectively, describe tap changing apparatus suitable for use with this invention.

In conventional tap changing apparatus, the vacuum switches are usually allowed to remain connected to the tapped winding while the switch is open after a tap change. This allows an electric field to exist across the vacuum switch and allows winding voltage surges to be applied to the vacuum switches. Therefore, it is desirable, and it is an object of this invention, to provide a load tap changer wherein open vacuum switches are not connected across the tapped winding after a tap change. It is also desirable, and it is another object of this invention, to provide a load tap changer wherein open vacuum switches are bypassed by the load trans fer switch after a tap change, thereby eliminating electric fields across the open vacuum switches.

SUMMARY OF THE INVENTION There is disclosed herein new and useful tap changing apparatus which removes the electric field from open vacuum switches and which also provides a bypass current path around the closed vacuum switches. The tap changing apparatus includes a multipleposition load transfer switch having a plurality of stationary and movable contacts. The stationary contacts are connected to vacuum switches and a current limiting impedance element. The movable contacts connect together a pair of stationary contacts. During a tap changing operation, the movable contacts change positions and the vacuum switches open and close in a predetermined sequence. When the tap change is completed, the movable contacts are in positions which bypass the open and closed vacuum switches and which disconnect one tap terminal from the open vacuum switches.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of this invention will become more apparent when considered in view of the following detailed description and drawings, in which:

FIG. 1 is a schematic diagram of a tapped winding and a load tap changer constructed according to this invention;

FIG. 2A is an elevational view showing the upper portion of a load tap changer constructed according to this invention;

FIG. 2B is an elevational view showing the lower portion of a load tap changer constructed according to this invention;

FIG. 3 is a top plan view of the movable and stationary contacts of a load transfer switch constructed according to this invention;

FIGS. 4-9 are schematic diagrams illustrating different positions of the load transfer switch duringa tap changing operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the following description, similar reference characters refer to similar members in all figures of the drawings.

Referring now to the drawings, and FIG. 1 in particular, there is shown a schematic diagram of a load tap changer constructed according to this invention. The tapped winding 20 includes the tap portions or terminals 3 through 19. An odd selector switch 22 includes a movable contact 24 which may be moved to connect to the odd numbered tap terminals. An even selector switch 26 includes a movable contact 28 which may be moved to connect the even numbered tap terminals. The load transfer switch'30 transfers the load from one selector switch to the other selector switch during a tap change. The reversing switch 32 includes the stationary contacts 34, 36, 37, 38, 39 and 40 and the movable contacts 42 and 44.

The function of the load transfer switch 30 is to connect the reversing switch 32 to either the odd selector switch 22 or to the even selector switch 26. The load transfer switch 30 must be capable of interrupting the current flowing to one selector switch and transferring the flow of load current to the other selector switch.

FIG. 2A shows the upper portion and FIG. 2B shows the lower portion of a load tap changer constructed according to this invention. The tap changing apparatus includes a support member 48 which may be constructed of an insulating material. The odd tap contacts, such as contact 11, the even tap contacts, such as tap contact 12, and the reversing switch stationary contacts, such as contact 34, are attached to the support member 48. The contacts ll, 12 and 34 include connectors 50, 52 and 54, respectively, which are suitable for connecting the necessary electrical leads to the contacts.

The odd selector switch 22 includes the insulated arm 56 which is attached to the shaft 58 by the collar 60$ A contact plate 62 is attached to the arm 56 and is constructed of a conducting material. The finger contact structure 64 is also attached to the insulated arm 56 and electrically connects the contact plate 62 to the tap terminals, such as tap terminal 11. A finger contact structure 66 is attached to the stationary terminal 68 and provides contact between the contact plate 62 and the stationary terminal 68. Stationary terminal 68 is electrically connected to the transfer switch 30 by suitable electrical conductors.

The shaft 58 extends through the bearing 72 which is secured by the end hood 74. The shaft 58 is rotated by the odd selector switch drive mechanism 76. As the shaft 58 is rotated, the insulated arm 56 and the contact plate 62 rotate to change the tap terminal which is connected to the stationary terminal 68. The drive mechanism 76 is constructed to rotate the shaft 58 in the proper direction and at the proper time in sequence with the other moving parts of the tap changing apparatus.

The even selector switch 26 includes the insulating arm 78, the contact plate 80, the finger contact structures 82 and 84, and the stationary terminal 86, all of which are constructed similar to the components of the odd selector switch 22. The insulating arm 78 is attached to the shaft 90 by the collar 92. Shaft 90 is coaxially positioned around the shaft 58 and is secured by the bearing 94. The shaft 90 is rotated by the even selector switch drive mechanism 96. As shaft 90 rotates, the insulated arm 78 and the contact plate 80 rotate to change the tap terminal which is connected to the stationary terminal 86. The stationary terminal 86 is electrically connected to the transfer switch 30 by suitable electrical conductors.

The reversing switch 32 includes a drum support 98 which is attached to the drum braces 100 and 102. The drum brace 100 contains an opening 104 through which the shafts 58 and 90 extend. The drum brace 102 is supported from the shaft 90 by the bearing 106. The

.drum brace 102 includes a shaft 108 which is positioned coaxially with the shafts 58 and 90. The shaft 108 is rotated by the reversing switch drive mechanism 112. Satisfactory construction materials, such as a conducting material for the drum brace 102 and the shaft 108, and an insulating material for the drum brace 1.00 and the drum support 98, may be used.

The support member 48 is secured to a housing structure 122 which houses the lower ends of the shafts 58, 9.0 and 108 and the drive mechanisms 76,96 and 112. The housing, structure 122 is mounted on top of the frame structure 124 which, as shown in FIG. 2B, is supported from the transformer casing 126 by suitable insulators, such as the insulator 128. The input shaft 130 controls the drive mechanisms 76,96 and 112 and is rotated by a prime mover through the gear box 132, the universals 134 and 136, and the coupling insulator 138. Thus, the potential on the portion of the tap changing apparatus which is located above the insulators 128 and 138 is isolated from the transformer casing 126.

The transfer switch 30 is physically positioned within the frame structure 124. The transfer switch 30 in this embodiment includes a plurality of finger contact structures, such as the finger contact structures 140 and 142. The finger contact structures are attached to base plates 143 and 145 and are electrically connected in parallel circuit relationship with each other to provide adequate current capability.

FIG. 3 is a top plan view of the lower portion of the transfer switch 30. The base plate 145 is constructed of an insulating material and is attached to the shaft 147. The finger contact structures 142, 150, 152, 154, 156 and 158 are attached to the base plate 145 and engage with the conductor bars 160, 162 and 164. The finger contact structures 142 and 150 and the conductor bar 160 form a movable contact 171 which is moved when the shaft 147 is rotated. The other finger contact structures and conductor bars form additional movable contacts 173 and 175.

Stationary contacts l66, 168, 170, 172 and 174 are constructed of conductor blades which are attached to contact mounting members, such as member 186. The electrical leads 176, 178, 180, 182 and 184 electrically connect the stationary contacts to other components of the tap changer. The contact mounting members are constructed of a conducting material and are attached to the insulating supports 200, 202, 204, 206 and 208. Respective stationary contacts in the upper and lower portions of the transfer switch 30 are connected together by the contact mounting members.

The transfer switch 30 also includes current interrupting means such as the vacuum switches 144 and 146 and an additional vacuum switch 188 which is not illustrated in FIG. 2B. The vacuum switches and the movable contacts of the transfer switch 30 are moved by the drive mechanism 148 which is driven by the rotation of the shaft 130. The mechanical motion provided by the drive mechanism 148 moves the components of the transfer switch 30 in the proper sequence with the other moving parts of the tap changer. FIGS. 4-9 illustrate schematically the operation of the transfer switch 30 during a tap change.

Referring to FIG. 4, the even selector switch is on tap terminal 16 of the tapped winding 20. The odd selector switch is on tap terminal 17. The sequence of operations described herein changes the tap position from tap terminal 17 to tap terminal 16.

In tap position 17, the load current i flows through the stationary contact 170, the movable contact 173, the stationary contact 172, the movable contact 175, the stationary contact 174 and the odd selector switch movable contact 24 to tap terminal 17. Some load current flows through the vacuum switch 146 and a small amount of load current flows through the vacuum switch 188 and the impedance 190, which may be a power resistor. It is pointed out that the vacuum switch 144 is disconnected from tap terminal 16 and is shunted by the movable contact 171.

The first step in providing a tap change is to rotate the base plate to which the movable contacts 171, 173 and 175 are attached in the direction indicated by the arrow 192 to provide the second position of the multiple position load transfer switch 30. Although the operation is described with reference to the lower base plate and contacts, the operation of the upper base plate and contacts is similar. Upon rotation, the movable contact 173 disconnects the stationary contact from the stationary contact 172. In addition, the movable contact 171 disconnects the stationary contact 168 from the stationary contact 170 and connects the stationary contact 166 to the stationary contact 168. In this configuration, as shown in FIG. 5, the load current is mainly flowing through the vacuum switch 146, the stationary contact 172, the movable contact 175, the stationary contact 174, and the contact 24 of the even selector switch to tap terminal 17. A small amount of current flows through the vacuum switch 188 and the impedance 190.

FIG. 6 illustrates the next position of the load transfer switch 30 in providing a tap change. Vacuum switch 146 is opened and the load current flows through the vacuum switch 188, the impedance 190, the stationary contact 172, the movable contact 175, the stationary contact 174, and the movable contact 24 to tap terminal 17. Then, vacuum switch 144 is closed as shown in FIG. 7. With this configuration, the load current flows mainly through the vacuum switch 144, the stationary contacts 166 and 168, the movable contacts 171 and 28, to tap terminal 16. Tap-to-tap current is limited by the impedance 190. The vacuum switch 188 is then opened as shown in FIG. 8. This configuration eliminates the tap-to-tap currents completely.

FIG. 9 illustrates the final position in providing a tap change. The movable contacts 171, 173 and 175 have been rotated in the direction indicated by the arrow 192 from the position shown in FIG. 8. In addition, the movable contact 24 of the odd selector switch has been moved from tap terminal 17 to tap terminal in preparation for the next tap change. It is pointed out that vacuum switches 146 and 188 are disconnected from tap terminal 15 and are shunted by the movable contact 175.

When the tap changer has completed a tap change, the electric field across all of the vacuum switches is eliminated. The next tap changing operation is performed by the same load transfer switch movements, except that they are in reverse sequence. Thus, during tap changes, the load transfer switch rotates in an oscillating manner, that is, it rotates in one direction during one tap change and in the opposite direction during the next tap change.

Since numerous changes may be made in the above described apparatus, and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all of the matter contained in the foregoing description, or shown in the accompanying drawings, shall be interpreted as-illustrative rather than limiting.

I claim as my invention:

1. Tap changing apparatus comprising:

first and second tap selecting means;

first, second and third current interrupting means each having first and second terminals;

means for opening and closing said first, second and third current interrupting means;

first, second, third, fourth and fifth stationary contacts, said first stationary contact being connected to said first tap selecting means, said fifth stationary contact being connected to said second tap selecting means, the second terminal of said second current interrupting means being connected to said second stationary contact, the second terminal of said third current interrupting means being connected to said fourth stationary contact, and the first terminals of said first, second and third current interrupting means being connected to said third stationary contact; impedance means electrically connected between said second stationary contact and the second terminal of said first current interrupting means; first, second and third movable contacts; and means for moving said first, second and third movable contacts in unison to first, second, third, fourth and fifth positions, said movable contacts connecting together appropriate stationary contacts in each position to maintain a current path between one of said tap selecting means and the first terminals of said first, second and third current interrupting means.

2. The tap changing apparatus of claim I wherein the first tap selecting means moves to a different tap terminal when the movable contacts move from the fifth position to the sixth position.

3. The tap changing apparatus of claim 2 wherein, when the movable contacts are in the first position, the first movable contact electrically connects together the first and second stationary contacts, the second movable contact electrically connects together the second and third stationary contacts, the third movable contact electrically connects together the third and fourth stationary contacts, the first and second current interrupting means are closed, and the third current interrupting means is open.

4. The tap changing apparatus of claim 2 wherein, when the movable contacts are in the second position, the first movable contact electrically connects together the first and second stationary contacts, the third movable contact electrically connects together the fourth and fifth stationary contacts, the first and second current interrupting means are closed, and the third current interrupting means is open.

5. The tap changing apparatus of claim 2 wherein, when the movable contacts are in the third position, the first movable contact electrically connects together the first and second stationary contacts, the third movable contact electrically connects together the fourth and fifth stationary contacts, the first current interrupting means is closed, and the second and third current interrupting means are open.

6. The tap changing apparatus of claim 2 wherein, when the movable contacts are in the fourth position, the first movable contact electrically connects together the first and second stationary contacts, the third movable contact electrically connects together the foruth and fifth stationary contacts, the first and third current interrupting means are closed, and the second current interrupting means is open.

7. The tap changing apparatus of claim 2 wherein, when the movable contacts are in the fifth position, the first movable contact electrically connects together the first and second stationary contacts, the third movable contact electrically connects together the fourth and fifth stationary contacts, the first and second current interrupting means are open, and the third current interrupting means is closed.

8. The tap changing apparatusof claim 2 wherein, when the movable contacts are in the sixth position, the first movable contact electrically connects together the second and third stationary contacts, the second movable contact electrically connects together the third and fourth stationary contacts, the third movable contact electrically connects together the fourth and fifth stationary contacts, the first and second current interrupting means are open, and the third current interrupting means is closed. 

1. Tap changing apparatus comprising: first and second tap selecting means; first, second and third current interRupting means each having first and second terminals; means for opening and closing said first, second and third current interrupting means; first, second, third, fourth and fifth stationary contacts, said first stationary contact being connected to said first tap selecting means, said fifth stationary contact being connected to said second tap selecting means, the second terminal of said second current interrupting means being connected to said second stationary contact, the second terminal of said third current interrupting means being connected to said fourth stationary contact, and the first terminals of said first, second and third current interrupting means being connected to said third stationary contact; impedance means electrically connected between said second stationary contact and the second terminal of said first current interrupting means; first, second and third movable contacts; and means for moving said first, second and third movable contacts in unison to first, second, third, fourth and fifth positions, said movable contacts connecting together appropriate stationary contacts in each position to maintain a current path between one of said tap selecting means and the first terminals of said first, second and third current interrupting means.
 2. The tap changing apparatus of claim 1 wherein the first tap selecting means moves to a different tap terminal when the movable contacts move from the fifth position to the sixth position.
 3. The tap changing apparatus of claim 2 wherein, when the movable contacts are in the first position, the first movable contact electrically connects together the first and second stationary contacts, the second movable contact electrically connects together the second and third stationary contacts, the third movable contact electrically connects together the third and fourth stationary contacts, the first and second current interrupting means are closed, and the third current interrupting means is open.
 4. The tap changing apparatus of claim 2 wherein, when the movable contacts are in the second position, the first movable contact electrically connects together the first and second stationary contacts, the third movable contact electrically connects together the fourth and fifth stationary contacts, the first and second current interrupting means are closed, and the third current interrupting means is open.
 5. The tap changing apparatus of claim 2 wherein, when the movable contacts are in the third position, the first movable contact electrically connects together the first and second stationary contacts, the third movable contact electrically connects together the fourth and fifth stationary contacts, the first current interrupting means is closed, and the second and third current interrupting means are open.
 6. The tap changing apparatus of claim 2 wherein, when the movable contacts are in the fourth position, the first movable contact electrically connects together the first and second stationary contacts, the third movable contact electrically connects together the foruth and fifth stationary contacts, the first and third current interrupting means are closed, and the second current interrupting means is open.
 7. The tap changing apparatus of claim 2 wherein, when the movable contacts are in the fifth position, the first movable contact electrically connects together the first and second stationary contacts, the third movable contact electrically connects together the fourth and fifth stationary contacts, the first and second current interrupting means are open, and the third current interrupting means is closed.
 8. The tap changing apparatus of claim 2 wherein, when the movable contacts are in the sixth position, the first movable contact electrically connects together the second and third stationary contacts, the second movable contact electrically connects together the third and fourth stationary contacts, the third movable contact electrically connects together the fourth and fifth stAtionary contacts, the first and second current interrupting means are open, and the third current interrupting means is closed. 